An apparatus for excavating a substantially vertical slot in the ground as a step in making a sealing wall or a supporting wall generally comprises a frame member, a supporting shield, at least two cutting wheels and a drive unit.
The supporting shield is attached to the frame member and carries the cutting wheels and the drive unit. Further the cutting wheels are mounted on a common shaft and a portion of the drive unit is enclosed by a cutting wheel. The supporting shield can be connected pivotally to the frame member (German Open Patent Application DE-OS No. 36 02 387).
The drive motors are placed above the supporting shield in the frame member in the apparatus according to German Open Patent Application DE-OS No. 34 24 999. Transmission elements extend from this drive motor through holes and recesses in the supporting shield to the region of the axis of the cutting wheels.
Other gear elements or drive elements also are located in openings and recesses in the supporting shield. The holes or recesses are made larger for cutting wheels with larger drive torques. This reduces the polar moment of inertia of the supporting shield. However, to enable the increased load to be borne, the supporting shield must be stout. That is disadvantageous since a comparatively thick supporting shield with wide flank spacing and hence large interwheel spacing between the cutting wheels is required; this means that a broad web of earth remains between the wheels when they operate, thereby causing problems.